Spring.wmf (18300 bytes) Plant Physiology (Biology 327)  - Dr. Stephen G. Saupe;  College of St. Benedict/ St. John's University;  Biology Department; Collegeville, MN  56321; (320) 363 - 2782; (320) 363 - 3202, fax;    ssaupe@csbsju.edu

Stomatal Size

Background Information
    In this exercise we will measure the size of the stomatal apparatus of Broad bean (Vicia faba) using an ocular micrometer.  The length and width of the guard cells is reported to be approximately 45
μm and 30 μm, respectively.

    How large is the stomatal apparatus in our Broad bean plants?  Do stomata occur on both sides of the leaf?  Is there a difference in size of the stomatal apparatus on the abaxial and adaxial leaf surfaces?

    Guard cells and stomata will occur on both abaxial and adaxial surfaces.  The size of the guard cells will be 45 x 30


  1. Obtain a Broad bean plant.  Decide which leaflets to sample and where on an individual leaflet you will take your sample to insure uniformity of samples.

  2. Prepare three epidermal peels from the abaxial side of the leaf.

  3. Calibrate the ocular micrometer using a stage micrometer according to the instructions provided in class.  Record your data in Table 1.

  4. Measure the length and width of 10, randomly-selected guard cells on each strip with an ocular micrometer.  Record your data in Table 2.

  5. Repeat using three epidermal peels from the adaxial (upper) side of the leaf.


  1. Complete Table 2 by converting ocular micrometer units to μm

  2. Perform a paired t-test on your data.

  • Ho:

  • t statistic =

  • probability value =  


Table 1:  Ocular Micrometer Calibration Data  
Magnification Actual size of 1 ocular micrometer unit (μm)  


Table 2:  Measurements of stomatal apparatus in Broad bean measured on epidermal leaf peels with an ocular micrometer  


Abaxial Adaxial
Length Width Length Width
omu μm omu μm omu μm omu μm
Mean +/- std dev                


  1. How large is the stomatal apparatus in Broad bean?  Do your data support previously published reports? 

  2. Is there any difference in size between the abaxial and adaxial leaf surfaces?  Cite your statistical data to support your conclusion.  

  3. How do Broad beans compare to other species?  Is there a significant difference in size between broad bean and other species?

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Last updated:  01/07/2009     � Copyright  by SG Saupe